1. Field of the Invention
The present invention relates to a liquid ejection device including a liquid ejection head for ejecting a liquid and a method of suppressing the leakage of a liquid from the liquid ejection head.
2. Description of the Related Art
A liquid ejection device including a liquid ejection head (hereinafter simply referred to as “head”) has been known. In recent years, the liquid ejection device has been used in various fields, for example, in an inkjet recording device.
In the liquid ejection device including the head, when the pressure of a liquid in the head increases, the liquid leaks from an orifice of the head. The liquid leaking from the head may adversely affect a main body of the liquid ejection device. For this reason, it is required to maintain the internal pressure of the head to be a negative pressure.
In Japanese Patent Application Laid-Open No. 2006-192785, there is disclosed a liquid ejection device including a sealed housing (also referred to as “containing portion”) and an ink tank provided in the housing. The inside of the ink tank forms a first containing space for containing a liquid, and air is sealed in a second containing space formed between an outer side surface of the ink tank and an inner side surface of the housing.
Further, the head communicates with the ink tank so that the liquid contained in the ink tank is supplied to the head. The ink tank is a bag-shaped container having flexibility, and the volume of the containing bag changes along with the ejection of the liquid.
In addition, the liquid ejection device further includes a regulator for adjusting the pressure of gas in the second containing space, and the pressure of the liquid contained in the ink tank is adjusted when the regulator adjusts the pressure of the gas. As a result, the internal pressure of the head is maintained to be a negative pressure.
In Japanese Patent Application Laid-Open No. 2008-105360, there is disclosed a liquid ejection device including an ink tank and a housing. Further, a float filled with gas is provided between an outer side surface of the ink tank and an inner side surface of the housing, and a region therebetween is filled with a liquid filler for floating the float.
Specifically, the ink tank is fixed to a bottom wall of the housing, and the float is fixed to an upper part of the ink tank. The float is positioned in the liquid filler, and a buoyant force is generated in the float.
In the liquid ejection device, the ink tank is biased in a direction of enlarging the capacity of the ink tank by virtue of the buoyant force generated in the float. When the biasing force acts on the ink tank, the internal pressure of each of the ink tank and the head is maintained to be a negative pressure.
However, the liquid ejection device disclosed in Japanese Patent Application Laid-Open No. 2006-192785 has the following problems.
Specifically, the volume of air is liable to vary along with a change in temperature or pressure. The gas is sealed in the second containing space, and hence the volume of the gas sealed in the second containing space varies along with a change in temperature or atmospheric pressure on the periphery of the liquid ejection device. As a result, the pressure of the liquid in the ink tank may vary.
Further, the flexible member forming the ink tank is made of a material which is not capable of preventing the permeation of gas completely. Therefore, the gas sealed in the second containing space enters the ink tank to generate air bubbles in the liquid contained in the ink tank. The generation of the air bubbles in the liquid increases the pressure of the liquid.
Further, the first containing space is filled with the liquid and the second containing space is filled with the gas, and the difference in density between the liquid and the gas is relatively large. Therefore, the ink tank is rocked relatively greatly when an impact is applied to the housing. When the ink tank is rocked, the pressure of the liquid in the ink tank varies.
As described above, in the liquid ejection device, the pressure of the liquid contained in the ink tank is liable to vary. Therefore, it is difficult to maintain the internal pressure of the head to be a negative pressure, and there has been a risk in that the liquid may leak from the head.
On the other hand, in the liquid ejection device disclosed in Japanese Patent Application Laid-Open No. 2008-105360, the float filled with the gas is required to be sunk in the liquid filler. The difference in density between the gas and the liquid filler is relatively large, and hence the float is rocked relatively greatly when an impact is applied to the housing. The containing bag is rocked along with the rocking of the float, and the pressure of the liquid in the containing bag varies. As a result, the pressure of the liquid in the head varies, and there has been a risk in that the liquid may leak from the head.